Multistep Transitions Research Articles

Effect of pressure on the electrical resistivity of Ce 3SnC single crystal

New ternary compound Ce 3SnC has a simple face-centered cubic CaO 3Ti-type structure. We found that Ce 3SnC undergoes a transition to an antiferromagnetic state at T N =7.0 K and the magnetization process shows multi-step metamagnetic transitions at T=1.5 K . In this work, we present the effect of pressure on the electrical resistivity of Ce 3SnC. The anomaly which originates from antiferromagnetic ordering is observed around T N at 1 bar. The results reveal that T N increases drastically with increasing pressure up to P=23 kbar .

層状金属間化合物Ｇｄ１−ｘＬａｘＭｎ２Ｇｅ２の特異な磁性と伝導現象 （ＩＩ） Ｇｄ０．９２５Ｌａ０．０７５Ｍｎ２Ｇｅ２の示す多段階メタ磁性転移と巨大磁気抵抗

In this work, we studied the magnetic and transport properties of an intermetallic compound Gd0.925La0.075Mn2Ge2 with a ThCr2Si2-type layered structure. Gd0.925La0.075Mn2Ge2 exhibits canted ferrimagnetism with ferromagnetic and antiferromagnetic components below Tt1 = 348K. With decreasing temperature, it moves into a non-collinear antiferromagnetic state at Tt2 = 244 K, and finally transforms into a reentrant canted ferrimagnet at Tt3 = 142 K. For Tt3 < T < Tt2, a field induced metamagnetism from antiferromagnetism to ferrimagnetism occurs at relatively lower fields, accompanied with fractal like multi-step metamagnetic transitions, the so called “devil’s stair-case”. The appearance of such fractal like multi-step metamagnetic transitions may result from a step-like formation of ferrimagnetic clusters due to spin-flips of Mn moments that occur independently in the antiferromagnet when magnetic fields are applied as well as from a step-like growth of their ferrimagnetic clusters. In addition, a giant magnetoresistance effect (Δρ/ρ∼15%) was also observed at the metamagnetic transition.

Neutron diffraction study of triangular lattice antiferromagnet CuFeO 2 under high magnetic field

The first step of multi-step metamagnetic phase transitions of triangular lattice antiferromagnet (TLA) CuFeO 2 has been studied at 4.2 K by pulsed neutron diffraction technique with repeating pulsed magnetic fields up to 13 T. Corresponding to the metamagnetic phase transition from 4-sublattice ground state, (1/5,1/5,3/2) magnetic Bragg reflection is clearly observed, implying that the first field-induced state is a “5-sublattice-like magnetic state”, as predicted by a 2D Ising spin TLA model with competing exchange interactions up to third neighbors.

Multistep transitions in collagens

It is well known that collagens exist in triple-helical form, and, on average, the individual chains have glycine at every third place. Collagens from different sources vary in distributions of other amino acids. They could also be different in the distribution of defects, which are generally nonhelical regions of low stability. Varying lengths of individual chains in the triple-helical system can also contribute to this variability. All these variations manifest themselves in the creation of a transition profile with undulations that are indicative of a multiphasic nature. In the present communication, we try to understand this variability by using essentially the Zimm and Bragg approach and suitably amending it for a triple-helical system. Factors that contribute to the multiphasic nature are incorporated into the transition model and discussed. Results obtained for collagen types I, II, III, Vx, Vy, and XI are in agreement with the experimental measurements. Transitions in the first three types can be interpreted on the basis of two-phase theory. Nucleation parameters, which are indicative of the sharpness of transition, are interpreted in terms of stability and possible amino acid composition.

Pressure-induced magnetic transition in CeP

Pressure dependence of magnetization in CeP is investigated up to 2 GPa. Multi-step transitions are induced by pressure. An antiferromagnetic transition at T N = 11 K below 0.1 GPa develops into two (magnetic) transitions at T L and T H in the region of 0.1 < P < 1.3 GPa, and into three magnetic transitions at T L, T H and T d above 1.3 GPa. For decreasing temperature an abrupt increase of magnetization, M( T), has been observed below T H and a round maximum of magnetization appearss at T L for P ⩾ 0.4 GPa. Above 1.3 GPa, an anomalous decrease of M( T) begins at T d = 10 K. Using previously reported 31P-NMR shift data it is shown that the pressure dependence of a characteristic temperature, which is proportional to the crystal field splitting in the paramagnetic temperature region, decreases rapidly with increasing pressure.

Magnetic phase transitions and magnetoresistance in easy-plane antiferromagnets HoGa 2 and DyGa 2

The results of the magnetization and magnetoresistance studies performed on single crystals of hexagonal HoGa 2 and DyGa 2 compounds are presented. They have an antiferromagnetic alignment of the magnetic moments of R-ions in the basal plane below the Néel temperatures 7.6 and 11 K respectively. The field-induced multi-step magnetic phase transitions in the basal plane are accompanied by the great changes in the electrical resistivity of both compounds. Using data on the magnetoresistance, two field-induced intermediate phases in HoGa 2 are found, when the field was applied along the a axis, which is of easy magnetization. The magnetic phase diagram of HoGa 2 along a axes is determined.

Magnetic phase diagram of TbGa 2

Magnetization measurements on a single crystal, powder neutron diffraction experiments and specific heat on the hexagonal TbGa 2 compounds are presented. Below T N = 18.5 K, multistep metamagnetic transitions are observed when the field is applied perpendicular to the [001] hard magnetization axis. The H-T magnetic phase diagrams along the [100] and [120] directions were deduced. At any temperature below T N, the magnetic structure is described with the incommensurate propagation vector Q = ( 1 3 , 1 3 , 0.189) . From the neutron diffraction experiments three possible magnetic structures are deduced, among them a triangular structure modulated along c being the most likely.

Multistep transitions between Rydberg states of Na induced by blackbody radiation.

We report on measurements of the time dependence of the populations of Rydberg states of Na with n=25--33 produced by stepwise excitation or deexcitation from the initially populated state 28s, stimulated by room-temperature blackbody radiation. We also present a theoretical modeling of the experiments, which mainly consists of solving the set of coupled rate equations for all the states involved. The results of the calculations show that for times of the order of the lifetime of 28s the populations of ns and nd states produced via two-step transitions can be up to 30% of the populations of np states. We also find that np states get repopulated via three-step transitions at the 2--12 % level. A comparison between the data and calculations shows good agreement.

Magnetic properties of ErRu2Si2

We have performed specific heat, susceptibility, magnetization and neutron diffraction measurements on the antiferromagnetic compound ErRu2Si2 single crystals. Field-induced multi-step phase transitions are observed. The crystalline field energy levels and the magnetic structures as a function of magnetic field are obtained from the experimental results.

Thermal transition of plasmid pBR322 closed circular, open circular and linear DNAs

Thermal transitions of pBR322 closed circular (cc), open circular (oc) and linear (l) DNAs have been measured by calorimetry. Six or eight peaks were observed for l and oc DNAs in 0.1 × SSC and 1 × SSC buffer solutions in the temperature ranges 67–84°C and 82–97°C, respectively, while ccDNA showed one broad peak at 103°C. Thermal reversibility was excellent for 1DNA and good for ocDNA but the DSC curve of ccDNA at the consequent second heating was quite different from that of the first run. The morphological changes induced by heating cc and ocDNAs have been examined by electrophoresis of the preheated samples. ccDNA which was heated above 75°C was found to be converted partly to ocDNA, the amount of ocDNA increasing with increasing temperature. The DSC curve of lDNA in 0.1 × SSC has been deconvoluted to a 24-state transition, and thermodynamic functions for the multistep transitions have been estimated; the results are discussed in comparison with its theoretical melting curve and its genetic map.

Mechanism of the magnetization process of DyB 6

Magnetization of a single-crystal of dysprosium hexaboride, DyB 6, at 4.2 K shows multistep transitions with increasing external magnetic field. The multistep transitions are understood by a simple spin-flip model using a noncollinear triple k spin structure. The numerical analysis of the magnetization process is well fitted to the above model considering the exchange and Zeeman energy.

Structure of 14c studied by the 14c(p,d) 13c reaction

Cross sections for the neutron pickup reaction 14C(p, d) 13C were measured at E p = 35.0 MeV for the states below E = 10 MeV, and at E p = 40.1 MeV for the states between E x = 11 and 18 MeV. Obtained angular distributions were compared with exact finite-range DWBA calculations to extract spectroscopic factors. Second-order DWBA calculations were also made in some cases. Almost full 0p 1 2 strength was found, while the observed 0p 3 2 strength was 80% of the simple sum-rule limit. The main part of the remaining strength was found in the 0d 5 2 orbit, and, in a lesser degree, in the 1s 1 2 and 0d 3 2 orbits. Small fractions of the 0f 5 2 and Og 9 2 strengths were also necessary to explain the angular-distribution shapes and the cross-section magnitudes of the predominantly multistep transitions to the 5− 2 and 5+ 2 states.

Random walk in dynamically disordered chains: Poisson white noise disorder

Exact solutions are given for a variety of models of random walks in a chain with time-dependent disorder. Dynamic disorder is modeled by white Poisson noise. Models with site-independent (global) and site-dependent (local) disorder are considered. Results are described in terms of an affective random walk in a nondisordered medium. In the cases of global disorder the effective random walk contains multistep transitions, so that the continuous limit is not a diffusion process. In the cases of local disorder the effective process is equivalent to usual random walk in the absence of disorder but with slower diffusion. Difficulties associated with the continuous-limit representation of random walk in a disordered chain are discussed. In particular, we consider explicit cases in which taking the continuous limit and averaging over disorder sources do not commute.

Hadronic excitation of the second 0+ state in 90Zr.

Coupled-channel analyses of new (n,n') and existing (p,p') as well as (..cap alpha..,..cap alpha..') scattering measurements for the second 0/sup +/ state (1.761 MeV) in /sup 90/Zr are described. Macroscopic form factors are assumed for the E0 and E2 transitions. Multistep E2 transitions are found to dominate the direct inelastic excitations. Compound (n,n') and (p,p') scattering processes are also found to be important at incident energies up to 16 MeV. A rather good description of shapes and magnitudes of the differential cross sections is achieved.

Hole states excited by theMg24(p,d)Mg23reaction at 95 MeV

Experimental excitation energies and angular distributions have been obtained for 33 deuteron groups from the $^{24}\mathrm{Mg}$($p$,$d$) reaction at 94.8-MeV bombarding energy with 80-keV experimental resolution. Energies obtained for states in $^{23}\mathrm{Mg}$ are in agreement with the sixth compilation of Endt and van der Leun up to 7.25 MeV and the recent unpublished ($p$,$t$) study of Nann et al. up to 9.72 MeV. Energies are determined in the present work for 18 additional groups corresponding to excitations between 9.8 and 13.28 MeV. Angular distributions from 6\ifmmode^\circ\else\textdegree\fi{} to 88\ifmmode^\circ\else\textdegree\fi{} laboratory (momentum transfers up to 660 MeV/c) show characteristic oscillatory signatures for $l=0$ transitions and broad peaked nonoscillatory behavior for presumed multistep transitions. $l=1 \mathrm{and} 2$ transitions show a very similar exponential falloff with large momentum transfer, but they can be clearly distinguished by their small-angle behavior after division by an empirical exponential factor or by the dominant momentum transfer dependence from a plane-wave analysis. $l=1$ transitions are observed to deep-hole states at 8.91-, 9.02-, 9.67-, and 10.57-MeV excitation. The angular distributions also lead to very probable assignments of $\frac{5}{{2}^{\ensuremath{-}}}$ and $\frac{7}{{2}^{+}}$ to the 3.97- and 4.68-MeV states of $^{23}\mathrm{Mg}$, and are consistent with $\frac{9}{{2}^{+}}$ and $\frac{11}{{2}^{+}}$ assignments to the 2.71- and 5.45-MeV states. Distorted-wave Born approximation (DWBA) predictions using optical potentials from published elastic scattering results show rather good agreement with the shapes of the observed angular distributions for $l=2$ transitions, but spectroscopic factors vary by up to a factor of 3 depending on the deuteron potential employed. $l=0$ transitions are not fitted in either shape or position of the oscillations, which may be due to the fact that deuteron wave functions derived from elastic scattering are not accurate in the nuclear interior. Reasonable shapes are predicted by preliminary coupled-channel Born approximation (CCBA) analyses for transitions believed to proceed in two steps.NUCLEAR REACTIONS $^{24}\mathrm{Mg}$ ($p$,$d$), $E=94.8$ MeV; measured $\ensuremath{\sigma}(\ensuremath{\theta})$. $^{23}\mathrm{Mg}$ levels deduced $l$, $J$, $\ensuremath{\pi}$. $S$. DWBA analysis, resolution 80 keV, $\ensuremath{\theta}=6\ifmmode^\circ\else\textdegree\fi{}\ensuremath{-}88\ifmmode^\circ\else\textdegree\fi{}$, $\ensuremath{\Delta}\ensuremath{\theta}=2\ifmmode^\circ\else\textdegree\fi{} or 4\ifmmode^\circ\else\textdegree\fi{}$, ${E}_{x}=0\ensuremath{-}13.28$ MeV.

Stability of Proteins Small Globular Proteins

The chapter discusses the stability of proteins and presents the results obtained on small compact globular proteins, which represent one single cooperative system. Protein is a cooperative system and behaves in an all-or-none fashion. Sharp changes in the properties of a protein do not mean anything in themselves because sequential multistep transitions exhibit the same sharp sigmoidal changes in the observed parameters. The problem of stability of native proteins is closely connected with the problem of protein denaturation, as stability can be judged only by breaking the native structure—that is, denaturing protein by various treatments. The pH of the solution is one of the most important factors determining the state of a protein. Potentiometric titration of protein revealed that smooth changes are connected with the titration of groups with a pK not very different from that of free amino acids, while the gross conformational changes associated with pH denaturation are accompanied by the unmasking of buried groups. The chapter also discusses the temperature-induced changes in protein, denaturational and predenaturational changes in protein, thermodynamics of protein unfolding, and thermodynamic properties of protein.

Interference between multi-step transitions in exotic atoms

We discuss the interference effects due to coherent transitions involving more than one photon in exotic atoms. It is found that the populations are not influenced by this interference. In the case of muonic atoms there is an influence on the polarizations under specific conditions.

Quadrupole transfer strength for deformed rare-earth nuclei as studied with heavy-ion induced two-nucleon transfer reactions

The quadrupole transfer strength associated with the deformed pairing field has been studied by measuring ground-state rotational band angular distributions for the ( 12C, 14C) reaction on 154Sm, 182W and 186W. It is shown that, through competition between direct and multistep transitions involving intermediate inelastic excitation, reactions of this type may provide a useful means of studying an underlying structure description of deformed nuclei.

The 9Be(α, d) 11B reaction at Eα = 27 MeV

Angular distributions have been measured at E α = 27 MeV for the 9Be(α, d) reaction to the first seven states in 11B for the angular range 7.5°–120° c.m. Excitation curves have been measured in the energy range from 26.5 to 27.5 MeV in 100 keV steps at the lab angles 40°, 60° and 90°. No evidence for non-direct processes was observed. DWBA calculations with Cohen-Kurath spectroscopic amplitudes were moderately successful in describing the transitions to the 0, 2.12 and 5.02 MeV states. The transition to the 4.44 MeV state did not exhibit a stripping pattern and is characteristic of multi-step transitions.